Renewable electricity conversion of liquid fuels from hydrocarbon feedstocks

ABSTRACT

The present invention includes a method for converting renewable energy source electricity and a hydrocarbon feedstock into a liquid fuel by providing a source of renewable electrical energy in communication with a synthesis gas generation unit and an air separation unit. Oxygen from the air separation unit and a hydrocarbon feedstock is provided to the synthesis gas generation unit, thereby causing partial oxidation reactions in the synthesis gas generation unit in a process that converts the hydrocarbon feedstock into synthesis gas. The synthesis gas is then converted into a liquid fuel.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.15/267,021 filed Sep. 15, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/077,094 filed Nov. 11, 2013, issued as U.S. Pat.No. 9,469,533 on Oct. 18, 2016 which is a continuation of U.S. patentapplication Ser. No. 12/575,305, filed on Oct. 7, 2009, issued as U.S.Pat. No. 8,614,364 on Dec. 24, 2013 which is a continuation-in-part ofU.S. patent application Ser. No. 11/177,152, filed Jul. 6, 2005, nowabandoned, which further claims priority to U.S. Provisional ApplicationNo. 61/103,397, filed Oct. 7, 2008, and U.S. Provisional Application No.61/107,563, filed Oct. 22, 2008. These patents and applications areincorporated herein by this reference in their entirety and for anypurpose.

TECHNICAL FIELD

This invention relates to a system for optimal use of variableelectricity from a renewable energy source, such as from wind and solar,in the production of liquid fuels from various hydrocarbon feedstocks,and/or from water and from CO₂. The hydrocarbon-based feedstocks includemunicipal and industrial waste, biomass, coal and natural gas. Theliquids fuels that are produced include methanol, synthetic diesel andethanol.

In one aspect of the invention, the renewable energy source electricitypowers an oxygen separation unit which provides oxygen for partialoxidation conversion into synthesis gas. The synthesis gas may then beconverted into liquid fuels. The renewable energy source electricity isalso employed to power plasma and melter technologies which are used toenhance the conversion process. The system provides means to maintainliquid fuel production at a desired level by use of supplementalelectricity from nonrenewable sources and from storage of the oxygen Inaddition it provides the flexibility to operate at substantially reducedliquid fuel production levels. The cost of electricity used in thehydrocarbon to liquid fuel conversion facility is reduced by colocatingthe facility at a wind or solar energy farm. In addition, theelectricity cost is minimized by using surplus wind or solar electricitythat cannot be accommodated by a downstream load or by the electricaltransmission system. Embodiments that involve electrolytic and pyrolyticproduction of hydrogen are also described. In addition, landfill gas canbe used to provide power for the hydrocarbon to liquid fuel productionprocess.

BACKGROUND OF THE INVENTION

Wind and solar power can provide important new sources of electricitythat are renewable and do not contribute to greenhouse gas generation.However, these sources provide the electricity in a highly variablemanner. This makes it difficult to match the electricity production tothe needs of the electrical utilities that consume it. In addition, theelectrical transmission system capability will need to be increased inorder to move the electricity from where it is generated to where it isconsumed. A further issue is that electricity does not provide a meansto make a substantial reduction in petroleum use in the near term sinceit cannot be used to directly replace petroleum use in present cars andtrucks. A major switch to plug in hybrids and electric vehicles would berequired.

Various forms of storage of renewable electricity have been proposed todeal with the variability of production. They include pumped water andcompressed air. However, these approaches have substantial cost andscale issues, and are limited in location. Another approach that hasbeen suggested is to use the electricity to manufacture hydrogen asdiscussed below. None of these approaches provide easily substitutedfuels for petroleum based transportation fuels.

There is a substantial literature on concepts for the use of electricityfrom renewable sources for the generation of hydrogen including [M. Hsu,Renewable Energy operated Hydrogen Reforming System, InternationalPatent WO 2004/071947; Levene, J. I., M. K. Mann, R. Margolis, and A.Milbrandt, An Analysis of Hydrogen Production from Renewable ElectricitySources, National Renewable Energy Laboratory, Presented at ISES 2005Solar World Congress, Orlando, Fla., Aug. 6-12, 2005, NREL/CP-560-37612(2005); Bartholomy, O., Renewable Hydrogen From Wind In California,Proceedings, National Hydrogen Association, March 2005.

Some of these processes are electrolysis based. However, the purpose ofthese concepts is for a hydrogen-based economy. There are problems withdistribution, storage, use of hydrogen that in most cases are notacknowledged by the authors, and the common usage of electrolysisreleases the oxygen generated in the process rather than utilizing it ina beneficial way.

Use of renewable electricity to produce liquid fuels for transportationcan provide a means to both address the issue of the variability fromwind and solar energy and also convert it into an energy form which hasgreatest near term impact for reducing use of petroleum. The problem ofthe highly variable nature of electricity generation can be more easilyaddressed when the electricity is used in this manufacturing applicationrather than when it has to be matched to the needs of the electricalgrid.

Plasma technology offers a way for using electricity for conversion ofnatural gas and other hydrocarbon fuels into synthesis gas (syngas).Synthesis gas can then be used to make a variety of fuels. Conventionalthermal plasmas have been used. [CORMIER, J. M., RUSU I., Syngasproduction via methane steam reforming with oxygen: plasma reactorsversus chemical reactors: The future of technological plasmas, Journalof physics. D, Applied physics vol. 34, no 18, pp. 2798-2803 (2001); seealso Chun, Y. N., Kim, S. C., Production of hydrogen-rich gas frommethane by thermal plasma reform, Journal of the Air and WasteManagement Association, v 57, n 12, December, 2007, p 1447-1451]. Also,nonthermal plasma have been used [Nozaki, T., Tsukijihara, H., Fukui,W., Okazaki, K., Kinetic analysis of the catalyst and nonthermal plasmahybrid reaction for methane steam reforming, Energy and Fuels, v 21, n5, September/October, 2007, p 2525-2530; also, Ouni, F., Khacef, A.Cormier, J. M., Effect of oxygen on methane steam reforming in a slidingdischarge reactor, Chemical Engineering and Technology, v 29, n 5, May,2006, p 604-609]. Microwave discharges have also been suggested[Jasinski, M., Dora, M., Mizeraczyk, J., Production of hydrogen viamethane reforming using atmospheric pressure microwave plasma, Journalof Power Sources, v 181, n 1, Jun. 15, 2008, p 41-45]. The presentinvention overcomes these drawbacks of these approaches.

SUMMARY OF THE INVENTION

The present invention includes a method for converting renewable energysource electricity and a hydrocarbon feedstock into a liquid fuel. Oneaspect of the present invention operates by providing a source ofrenewable electrical energy in communication with a synthesis gasgeneration unit. An air separation unit is also provided incommunication with the synthesis gas generation unit. Electricity fromthe source of renewable electrical energy is then used to power the airseparation unit. As is common with renewable energy sources, theelectrical energy will typically vary over time. Oxygen from the airseparation unit and a hydrocarbon feedstock is also provided to thesynthesis gas generation unit, thereby causing partial oxidationreactions in the synthesis gas generation unit in a process thatconverts the hydrocarbon feedstock into synthesis gas. The synthesis gasis then converted into a liquid fuel. In this manner, it is possible toadjust the liquid fuel production level to a desired level when theamount of renewable source electricity is reduced. While not meant to belimiting, the source of renewable energy may be wind power or solarpower.

This embodiment of the present invention finds particularly advantageswhen the hydrocarbon feedstock is provided as municipal waste. Anotheraspect of the present invention is found when a variable amount ofelectricity from a second electrical source is provided to maintain theliquid fuel production at a desired level. While not meant to belimiting, it is preferred that the second electricity source is anengine generator, a gas turbine, a fuel cell, and combinations thereof.Also while not meant to be limiting, the second electricity source isfueled

Another aspect of the present invention that provides particularadvantages is when the source of renewable electrical energy, thesynthesis gas generation unit, the air separation unit, and the secondelectricity source are co-located. In such applications, particularadvantage is found when DC current is used to transmit power from therenewable energy electricity source to the synthesis gas generationunit.

The electricity from the renewable energy source may be used to power aplasma included in the synthesis gas generation unit, a joule heatedmelter included in the synthesis gas generation unit, or combinationsthereof. At least a portion of the oxygen produced by the air separationunit may also be stored for use at a later time. While not meant to belimiting, the air separation unit is preferably provided as a cryogenicseparation unit. Also while not meant to be limiting, the oxygenproduced in the air separation unit is preferably stored cryogenically.Another advantage of the present invention is the capability to vary therelative amounts of plasma heating, melter heating, oxygen and steamprovided in the synthesis gas generation unit in response to variationsin the amount of renewable energy source electricity. While not meant tobe limiting, it is preferred that the electricity to the joule heatedmelter included in the synthesis gas generation unit is reduced atdisproportionately smaller amount when the electricity input from therenewable energy source to the synthesis gas generation unit is reduced.The present invention may also include embodiments where at least someof the electricity from the renewable energy source is provided to atransmission system for use by a downstream user.

Another embodiment of the present invention replaces the air separationunit with an electrolysis unit. In an embodiment that includes andelectrolysis unit, at least a portion of the oxygen produced in theelectrolysis unit may be saved for use at a later time, and oxygenproduced in the electrolysis unit may be stored cryogenically. Whenutilizing an electrolysis unit, the present invention may produce liquidfuel by reacting CO₂ generated from the hydrocarbon feedstock withhydrogen produced in the electrolysis unit. In this type of arrangement,some of the renewable energy source electricity may be used forcompressing CO₂

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the embodiments of the inventionwill be more readily understood when taken in conjunction with thefollowing drawings, wherein:

FIG. 1 is a schematic diagram of hydrocarbon feedstock to liquid fuelconversion system using renewable energy electricity.

FIG. 2 is a schematic diagram of hydrocarbon feedstock to liquid fuelconversion system using variable electricity from non-renewable source(such as natural gas) to augment or replace renewable energyelectricity.

FIG. 3 is a schematic diagram of an electrical system for use of surplusrenewable electricity.

FIG. 4 is a schematic diagram showing the use of renewable electricityfor oxygen production for real time use in partial oxidation conversionof hydrocarbon feedstocks or for storage.

FIG. 5 is a graph showing the dependence of endothermicity on parameterA.

FIG. 6 is a schematic diagram showing the use of renewable ornon-renewable energy for electrolytical manufacturing of H₂ and O₂.

FIG. 7 is a schematic diagram showing a system for pyrolytic conversionof hydrocarbon feedstocks to liquid fuels. The system produces hydrogenby bubbling the hydrocarbon feedstock through a molten material. Thehydrogen is then reacted with CO₂ to produce a liquid fuel.

FIG. 8 is a schematic diagram showing a single pass reagents through aliquid fuel reactor, with unconverted reagents recycling tonon-renewable source of electricity instead of recycle to liquid fuelreactor

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitations of the inventivescope is thereby intended, as the scope of this invention should beevaluated with reference to the claims appended hereto. Alterations andfurther modifications in the illustrated devices, and such furtherapplications of the principles of the invention as illustrated hereinare contemplated as would normally occur to one skilled in the art towhich the invention relates.

It is the purpose of this invention to provide systems for improved useof electricity from renewable energy sources, such as wind or solarenergy, through the conversion of hydrocarbon feedstocks into a liquidfuel. The feedstocks include municipal and industrial waste, biomass,coal and natural gas. These systems can both reduce the cost ofproducing liquid fuels from hydrocarbon feedstocks and also decrease CO₂emissions.

The liquid fuels that can be produced include, but are not limited to,methanol (either as a fuel itself or as a feedstock for making DME orgasoline), ethanol, synthetic diesel (Fischer-Tropsch), aviation fuel,and combinations thereof.

Use of renewable energy sources can play an important role because ofthe relatively large amount of electricity that is used in presentprocesses that convert hydrocarbon feedstocks into liquid fuels. Theelectrical energy can be 10% to 15% of the chemical energy in the liquidfuel that is produced and the hydrocarbon chemical energy needed toproduce this electricity can thus approach 50% of the chemical energy ofthe liquid fuel. The primary use of the electricity is generally forproviding oxygen from air separation for partial oxidation conversion ofthese feedstocks into synthesis gas which is then converted into liquidfuels. It may also be used for various forms of electrical heating,including plasma heating and resistive heating of molten material, thatenhance the conversion process.

This invention involves systems which use renewable energy sources in anoptimal way to reduce the cost of electricity for production of liquidfuels from hydrocarbon feedstocks. The use of renewable electricity alsoreduces the amount of greenhouse gas that is generated in the productionof these fuels. The renewable energy source electricity is employed inways to achieve the greatest cost and CO₂ reductions. The systemsaccommodate the variable nature of the renewable electricity by optimaluse of additional electricity sources, and oxygen storage. They alsoinvolve hydrocarbon feedstock to synthesis conversion systems that havehigh turn down ratios (the ratio of maximum syngas production to minimumallowed production).

The system is shown in FIG. 1. The electricity is employed to providethe power for conversion of a hydrocarbon feedstock. The conversionprocess produces a synthesis gas (syngas), which is a mixture ofhydrogen and carbon monoxide. A preferred conversion process usespartial oxidation with oxygen produced by separation unit which ispartially or completely powered by the electricity from wind or solarenergy. The syngas is then converted by catalytic means into liquidfuels as shown in FIG. 1.

When the level of renewable electricity is reduced, because of thevariable nature of the source, the liquid fuel production plant can berun at a lower production level. Alternatively or in addition,replacement electricity from an onsite non-renewable gas powered sourcecould be used to achieve a desired level of plant operation as shown inFIG. 2. The non-renewable gas could include natural gas and syngas fromeither air blown or oxygen blown partial oxidation systems which usevarious feedstocks. The electricity could be provided by anengine-generator set, a gas turbine or a fuel cell. Another option, ifall that is needed to replace the renewable energy source electricity isheat, is to use combustion of non-renewable feedstocks to provide theenergy required for the process. In addition, as described below storedoxygen can also be used as a means to maintain the desired level ofliquid fuel production plant operation.

It is preferred that the liquid fuel production plant can be co-locatedat the wind turbine or solar energy site. In this way the cost oftransmitting the electricity is greatly reduced. There is also advantageof co-location in that the preferred manner to distributed theelectricity from the renewable to the syngas generator is through DC.Distributed electricity generation benefits from DC harnessing of theelectricity because AC generation can from multiple units is moredifficult to synchronize (from multiple wind turbines, for example), orgenerated DC, as is the case with photovoltaics. There is limited DCtransmission, and thus it would be best if the syngas generator is closeto the renewable energy source.

Thus there are a range of possibilities for using the supplementalnonrenewable energy source. The non-renewable energy could be used as aheat (i.e., combustion) in addition to, or instead of, generating theelectricity to be used in the process. The electricity could be used asthe source of energy for the process (for example as source of power forplasma heating) as well as for oxygen production. It could also be usedfor gas compression or gathering the CO₂ to be converted into methanolby reaction with hydrogen (from the atmosphere, separated from fluegases, etc.).

In one embodiment of the invention, some or all of the electricity fromthe renewable energy source is fed at some point in time into theelectrical grid for use in a downstream load. A schematic diagram of theoverall electrical system is shown in FIG. 3. FIG. 3a shows conditionswhere all the electricity generated by the renewable energy farm isconsumed by the downstream power load. All the electricity generated isfed to the transmission line. In case 3 b, not all the power that can begenerated by the renewable electricity farm is needed by the downstreamelectrical load or can be accommodated by the electrical transmissionsystem and thus there is extra power that cannot be fed to thetransmission line. In this case, the surplus electricity is used todrive the conversion of the hydrocarbon feedstock such as natural gas(which is mainly methane) to syngas followed by conversion of synthesisgas to a liquid fuel. The conversion of natural gas could beaccomplished by endothermic plasma reforming.

The electricity from the renewable energy sources could also be used topower an oxygen separation plant which provides oxygen for partialoxidation based conversion of natural gas or another hydrocarbonfeedstock into synthesis gas. The use of surplus electricity to power anoxygen separation unit could be in addition to or instead of it's inpowering a beat source for the process, as shown in FIG. 4. Theelectricity-driven heat source for the process could be a resistiveheater in the process, a plasma or an induction heater.

Both endothermic and exothermic plasma based reforming can be used. Theadvantage of endothermic plasma reforming is that there is no loss ofenergy as is the case in partial oxidation (which is an exothermicreaction). In the case of steam reforming of natural gas, plasmareforming avoids the need of consuming some of the natural gas to drivethe endothermic process. The energy required by the endothermic reactionis the surplus power from the renewable source. Operation close toautothermal reforming which uses partial oxidation combined with steamreforming or CO₂ reforming could increase the throughput of the methanolgeneration and allows flexibility of production of the liquid fuel. Theplasma energy increases the energy content of the synthesis gas.

Several options for conversion of hydrocarbon feedstocks to synthesisgas are available partial oxidation, steam reforming, CO₂ reforming,pyrolysis or a combination of the four. The first case is exothermic,with high temperatures, while steam reforming and CO₂ reforming areendothermic. Pyrolysis is also endothermic, although to a lower degreethan CO₂ or steam reforming. A combination of several of theseoperations would result in optimal synthesis gas for the methanolproduction, which calls ideally for a ratio of H₂ to CO of 2, for thereactionCO+2H₂→CH₃OH

In general, the reforming equation for natural gas that generates thisratio of H₂ to CO can be written as:A CH₄ +B CO₂ +C H₂O+D O₂→CO+2H₂where natural gas is represented by methane.

An additional constraint is that A, B, C, and D need to be positive(i.e., no removal of a compound). It can be easily shown thatB=1−AC=2−2AD=½(1−2B−C)=½(−3+4A)

For B, C, D>0, it is required that 1>A>¾.

Although the above example is for methanol production, there are othermeans of optimization of the feedstock for ethanol, or forethanol/methanol blends, and for heavier alcohols, such as butanol.However, methanol is by far the easiest one to produce, with highselectivity and efficiency, while ethanol is substantially lessselective (ethanol/methanol mixtures are generated in this case).

There is a range of O₂ addition that allows the reaction endothermicityto be varied (most endothermic for A=¾, that is, without the addition offree oxygen, to most exothermic for A=1, corresponding to partialoxidation), allowing the adjustment of the flow rate of synthesis gasfor a given power from the renewable source. The endothermicity as afunction of the parameter A in the above equations is shown in FIG. 5.At A>0.93, the reaction is exothermic, and heat is released. FIG. 5 iscalculated assuming thermal equilibrium at 25 bar and 1300 K, conditionsappropriate for generation of syngas from methane.

Methane conversion is high at these conditions. Whatever methane is leftcan be recycled before the catalyst which is used to convert the syngasto liquids, or after the catalyst, where simple condensation of theliquid fuel allows for the separation of the unconverted methane,

It is also possible to use electrolysis to generate both the hydrogenand oxygen required for all or some of the process, as shown in FIG. 6.The oxygen generated in the electrolysis process could be used in thesyngas generator or in other plants, also collocated, that use it togenerate syngas from various sources, including biomass and coal. Thusnot only is the hydrogen generated by the electrolysis useful, but so isthe oxygen, and it is not released to the atmosphere. The hydrogen canbe reacted with CO₂ from the gasification unit to produce liquid fueland reduce CO₂ emissions.

The possibility of using electrolyzers to augment the hydrogen in thesystem, or to provide all the hydrogen required, is attractive. Theadvantage of electrolyzer-based hydrogen generators is that they havelarge turn down ratios. The turn down ratio is much larger than that ofother large hydrogen production devices. The hydrogen and/or oxygencould be stored during times where the production exceeds the generatingcapability of the liquid fuel production plant, or the plant could bedesigned to manage the maximum hydrogen production. Similarly, theoxygen can be used or stored in a gasification plant next to theelectrolyzer units.

Turn down ratios of power as high as 2 have been determined forcatalyzed partial oxidation (CPO) [Dave, N. and G. A. Foulds,Comparative Assessment of Catalytic Partial Oxidation and SteamReforming for the Production of Methanol from Natural Gas, Ind. Eng.Chem. Res. 34, 1037-1043 1037 (1995)]. It should be noted that for theapplication of the present invention, the advantage is not necessarilyjust the minimization of the electrical power requirement, as it isneeded to use some of it in order to increase the heating value of themethanol and thus use it to “store” the electrical energy provided bythe renewable electricity generator. This is the case both for thesynfuel generator as well as the methanol or liquid fuel stages in theprocess.

Large plants that minimize the cost of manufacturing and the efficiencyof conversion use large scale, with limited turn down ratio, as thespace velocity of the compounds needs to be constant. These large plantsuse single train to obtain advantages of scale. In order to provide therequired turn down ratio, it is necessary to operate the liquid fuelout-of-optimal range. Thus, the use of energy from both the renewablesource as well as the one non-renewable source to maintain the optimalperformance of the liquid fuel plant results in improved performance.However, during times of off-optimal performance, the throughput of theplant should be varied. By using an inexpensive source of energy formost of the process, the increased relative cost of the methanolproduced during non-optimal times does not affect the overall economicsof the plant.

There are other ways to maintain constant productivity of the plant. Forexample, the rate of production of synthesis gas for optimal generationof methanol can be adjusted, for a given power, by adjusting theconcentration parameters indicated about (varying A). Alternatively, therate of synthesis gas generation can be adjusted by varying theelectrical power provided by the renewable energy source, at constantconcentration parameters.

By using an electricity-driven reformer, and in particular, plasmadriven reformers, it is possible to stabilize the synthesis gasgenerating unit. Conventional synthesis units have very narrow operatingparameters. In a preferred embodiment, the electricity is introducedinto the reaction chamber by a plasma discharge. The use of electricallyheated molten material in conjunction with a partial oxidation processcan also be used to stabilize operation and provide a high turn downratio. The molten material can be kept hot with a small amount ofelectricity and can be a very effective way to run the system at idle.The molten material can be kept hot as the liquid fuel production rateis decreased by increasing the percentage of total electricityconsumption that is used for joule or inductive heating of the melter.

For optimal plasma operation, the region of the electrodes can beprotected by a sheath gas, especially in the case with substantialamounts of steam. This not only minimizes the erosion, it also minimizesthe coking of the electrodes by the natural gas. In the case ofsubstantial amounts of steam, the discharge results in very aggressiveconditions that rapidly erode the electrodes. The plasma discharge couldbe AC or DC. However, DC is preferred for plasma stability. Also, DCfits better the power conditioning equipment, as most renewable powersources would generate DC either directly (as in the case ofphotovoltaics) or downstream, (as is the case of wind farms, if it isnot possible to synch the AC power produced by the multiple windmills,thus the electricity from each windmill needs to be rectified beforecombining its power with the power from the other units in the windfarm).

The production and use of oxygen can be varied so as to optimize theoverall system performance. The oxygen can either be consumed as it isproduced or stored using cryogenic storage. Cryogenic separation isattractive, as it is much easier to store during periods of high surpluspower, as compared with membrane separation, which requires much largervolume, even at high pressures. The stored oxygen could be used toprovide a buffer in the methane to syngas part of the plant in order toprovide continued operation when there is no surplus energy to drive theendothermic reaction. When there is reduced electrical power, thestoichiometry in the above chemical reaction is varied (relative amountsof oxygen and steam and/or CO₂ are changed), increasing the relativeamount of oxygen to make up the lack of electrical power.

The oxygen produced from the renewable electricity could also be used inpartial oxidation processes for conversion of hydrocarbon feedstocks tosyngas that do not involve the use of plasma, or partially involve theuse of a plasma.

Pyrolysis processes can be used for the manufacturing of hydrogen andother products. Plasma heating can be used, with substantial yields ofC₂ compounds (including acetylene), especially when including quenching.

In addition, a very attractive new alternative for using pyrolysis toproduce a hydrogen-rich gas is to bubble methane or natural gas througha liquid material where the heat required form the pyrolytic process issupplied by plasma heating or by electrical resistance heating in thematerial as shown in FIG. 7. Use of molten glass is particularlyattractive. Heat needs to be supplied to the molten material because thereaction is endothermic. The electrical heating can be supplied withelectrodes submerged in a molten glass bath (Joule heating), throughinductive heating using eddy currents, or a combination of the thesemethods each other or with plasma heating.

The pyrolysis reaction will separate the carbon from the methaneresulting in gas that is mainly hydrogen. The hydrogen can then bereacted with CO₂ to form synthesis that is then used to produce variousliquid fuels. The consumption of CO₂ can offset the generation of CO₂which is released in when energy is extracted from the liquid fuel bycombustion.

Methane pyrolysis in molten metals has been discussed previously [See,for example, Lewis, M. A. Serban, M., Marshall, C. L. and Lewis, D.,Direct Contact Pyrolysis Of Methane Using Nuclear Reactor Heat, ArgonneNational Laboratory, 2001.] In contrast, this new approach would useelectrical heating. Moreover, one embodiment would involve heating of aglass bath. Surplus electricity from the renewable energy source is usedto provide the energy to the molten liquid required for the endothermicreaction. There are also potential advantages of using slags resultingfrom waste processing as the molten liquid that drives the pyrolysis,allowing the generation of carbon-based products in the slag.

Through this method it is possible to sequester the carbon from naturalgas coal or another hydrocarbon fuel in a manner that is much morestraight forward than is the case when the carbon is combusted whichrequires capture and sequestration of CO₂, a more challenging endeavor.The additional hydrogen is produced in this process that can shift thebalance of oxygen, carbon and hydrogen to that which optimizes theproduction of the liquid fuels. This would allow the use inmanufacturing of liquid fuels with high hydrogen content from feedstocksthat are hydrogen poor. However, that the energy yield of the system islower than then if the carbon is combusted.

A further feature of this process is that full conversion of thehydrocarbon fuel to hydrogen and carbon is not needed. The unconvertedmethane can be converted into synthesis gas in a downstream unit and thesynthesis gas can then be converted into liquid fuels.

There are also potential methods for direct methanol generation throughthe use of nonthermal plasma discharges. [See, for example, Hijikata, K,Ogawa, K., Miyakawa, N., Methanol conversion from methane and watervapor by electric discharge (effect of electric discharge process onmethane conversion), Heat Transfer—Asian Research, 28, n 5, 1999, p404-417]. In this case, either corona or dielectric barrier dischargesare used to converted the mixture to methanol. Although this techniqueis substantially more power intensive than the direct conversion usinghigh temperature, the advantage of this technique is very rapid responseto the varying characteristics of the both the downstream use of theelectricity or the varying generation of the power source (due for, forexample, varying wind power).

The economics for these methods of employing renewable electricity toproduce liquid fuels are attractive because the electricity cost is low.The cost of electricity could in fact be negative when the renewableenergy source produces energy that exceeds what the electricitydispatcher asks for. Moreover, there is minimal electricity transmissionsystem cost for the synthesis or hydrogen gas generation unit. While themost economically attractive approach is to use surplus renewableelectricity that cannot be sent to the grid for downstream use, it is,also possible to use a greater fraction or all of the renewablegenerated electricity.

The system could be used to increase the use of stranded natural gaswhich cannot be transported to the end user by pipe line.

Another advantage of using renewable energy, such as windpower, is thatthe greenhouse gas emissions from converting natural gas into a liquidfuel are significantly reduced.

This approach for using excess renewable energy could also be employedin conjunction with electricity from geothermal energy. In addition, itcould be applied to the utilization of unused heat in solar thermalplants prior to conversion to electricity. The heat could be used toprovide the energy for a liquid used for the endothermic pyrolyticconversion of natural gas which is bubbled through it. A variation ofthis process is the use of both excess solar thermal energy andelectricity from another source to heat the liquid.

When methane is mentioned as a hydrocarbon feedstock in the abovediscussion, it is meant to cover both natural gas or gas streams thatcontain substantial amounts of natural gas. Also included are tail gasesfrom processing plants, producer gas, natural gas produced in oildrilling or landfill gas. In addition, it is possible to use solid orliquid hydrocarbons as the feedstock for the renewable energyelectricity plasma reforming process, partial oxidation processes whichuse the electricity to power an oxygen separation unit, or a pyrolysisunit. These hydrocarbons include municipal and other forms of waste,coal, various forms of biomass and various forms of petroleum. In theseapplications natural gas generated electricity could be used to augmentthe electricity generated by wind or solar power.

A complimentary approach is to use a single pass of the synthesis gasthrough the catalyst. Because conversion is not 100%, a substantialamount of the reagents are left unconverted. This is due to the factthat even at equilibrium there may be substantial amounts of unconvertedreagents, or that the system does not reach equilibrium. In this case,the conventional technique is to separate the liquid fuels, and thenrecompress and recycle the unconverted reagents. An alternative approachis to use the unconverted reagents to drive the external electricitysource, avoiding both the capital equipment and the power required forrecompressing and recycling the unconverted flows. FIG. 8 shows aschematic diagram of the concept.

Landfill gas, which consists of methane and a relatively small amount ofother hydrocarbon gases, may be a particularly attractive source ofelectricity production for waste to liquid fuels production facilitiessince existing landfills are preferred locations for these facilities.The landfill gas generated electricity can be used instead of wind andsolar generated electricity in the applications described above. Thelandfill gas can be converted into electricity by an engine-generatorset, a gas turbine or a fuel cell. The electricity can then be used topower an oxygen separation unit, plasma heating and/or a melter, orsolar electricity generation. In addition to providing liquid fuels thelandfill gas electricity powered system could also be used to producehydrogen.

A combination of landfill gas generated electricity and wind or solargenerated electricity could also be used to provide electricity for theliquid fuels from waste facility. The amount of landfill generatedelectricity could be varied so as to compensate for the variation inwind or solar generated electricity. The rate of gas extraction from thelandfill can be controlled so as to compensate for the changes in windor solar electricity generation. In order to minimize electricitytransmission cost, the solar or wind electricity generation facility canbe located at or adjacent to the landfill.

In a related application that does not involve a liquid fuels from wastefacility, control of landfill gas extraction (or extraction of methanefrom other sources such as a natural gas production well or storagefacility) for conversion into electricity can also be used to provide adesired level of electricity for sale from an electricity generationsystem that includes a variable electricity source such as wind or solarenergy. The outputs of engine generator sets, gas turbines and fuelcells can be rapidly varied so as to employ landfill or other gas basedelectricity generation to compensate for changes in wind or solarpowered electricity generation. In order to minimize electricitytransmission cost, the solar or wind electricity generation facility canbe located at or adjacent to the methane source.

In another embodiment the amount of landfill gas based electricity canbe controlled when used in combination with electricity from the grid soas to minimize the overall electricity cost for the liquid fuel fromwaste conversion facility by using a larger relative amount ofelectricity from the grid at times when it is available at a lowerprice.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character. Only certain embodimentshave been shown and described, and all changes, equivalents, andmodifications that come within the spirit of the invention describedherein are desired to be protected. Any experiments, experimentalexamples, or experimental results provided herein are intended to beillustrative of the present invention and should not be consideredlimiting or restrictive with regard to the invention scope. Further, anytheory, mechanism of operation, proof, or finding stated herein is meantto further enhance understanding of the present invention and is notintended to limit the present invention in any way to such theory,mechanism of operation, proof, or finding.

Thus, the specifics of this description and the attached drawings shouldnot be interpreted to limit the scope of this invention to the specificsthereof. Rather, the scope of this invention should be evaluated withreference to the claims appended hereto. In reading the claims it isintended that when words such as “a”, “an”, “at least one”, and “atleast a portion” are used there is no intention to limit the claims toonly one item unless specifically stated to the contrary in the claims.Further, when the language “at least a portion” and/or “a portion” isused, the claims may include a portion and/or the entire items unlessspecifically stated to the contrary. Likewise, where the term “input” or“output” is used in connection with an electric device or fluidprocessing unit, it should be understood to comprehend singular orplural and one or more signal channels or fluid lines as appropriate inthe context. Finally, all publications, patents, and patent

applications cited in this specification are herein incorporated byreference to the extent not inconsistent with the present disclosure asif each were specifically and individually indicated to be incorporatedby reference and set forth in its entirety herein.

What is claimed is:
 1. A method of producing synthesis gas, the methodcomprising: generating oxygen in an oxygen separation unit utilizingelectricity that is produced by a first electricity source where thefirst electricity source is a renewable energy source; supplying theoxygen from the oxygen separation unit to a synthesis gas generationunit; supplying steam to the synthesis gas generation unit; andproducing synthesis gas in the synthesis gas generation unit by reactinga hydrocarbon feedstock with the steam and the oxygen using acombination of steam reformation and partial oxidation in the synthesisgas generation unit.
 2. The method of claim 1 further comprising storingoxygen generated in the oxygen separation unit for future use when lesselectricity is available from the first electricity source.
 3. Themethod of claim 2 wherein storing the oxygen generated in the oxygengeneration unit includes cryogenically storing the oxygen generated inthe oxygen generation unit.
 4. The method of claim 2 further comprisingvarying an amount of stored oxygen used in the synthesis gas generationunit responsive to variation of an amount of electricity from the firstelectricity source.
 5. The method of claim 1 wherein generating oxygenin an oxygen separation unit utilizing electricity that is produced by afirst electricity source includes producing plasma in the synthesis gasgeneration unit with the electricity from the first electricity source.6. The method of claim 1 further comprising electrically heating amolten bath in the synthesis gas generation unit using electricity fromthe first electricity source.
 7. The method of claim 1 furthercomprising utilizing the electricity from the first electricity sourcefor compression of synthesis gas.
 8. The method of claim 1 furthercomprising utilizing electricity from a second electricity source forone or more of oxygen separation, plasma production in the synthesis gasgeneration unit, electrical heating of a molten bath in the synthesisgas generation unit, or synthesis gas compression when an amount ofelectricity that is provided by the first electricity source is reduced.9. The method of claim 8 where the second electricity source includesone or more of an engine generator, a gas turbine, or a fuel cell,wherein the engine generator, the gas turbine, or the fuel cell isconfigured to use methane as a fuel.
 10. The method of claim 9 where themethane is provided from landfill gas.
 11. The method of claim 1 furthercomprising converting the synthesis gas into a fuel.
 12. The method ofclaim 11 where the fuel is a liquid fuel.
 13. A method comprising:producing a fuel using partial oxidation of a hydrocarbon feedstock in asynthesis gas production unit, wherein producing the fuel includes:providing oxygen and hydrogen to the synthesis gas generation unit froman electrolysis unit; powering the synthesis gas production unit and theelectrolysis unit from a first electricity source including a renewableenergy source; and storing oxygen for later use in the synthesis gasgeneration unit when an amount of electricity from the first electricitysource is reduced.
 14. The method of claim 13 further comprisingproducing oxygen by oxygen separation using electricity from the firstelectricity source.
 15. The method of claim 13 storing oxygen for lateruse in the synthesis gas generation unit includes cryogenically storingthe oxygen.
 16. The method of claim 13 further comprising usingelectricity from a second electricity source to provide electricity tothe electrolysis unit when the electricity from the first electricitysource is reduced.
 17. The method of claim 16 wherein the secondelectricity source includes one or more of an engine generator, gasturbine, or fuel cell, wherein the engine generator, the gas turbine, ofthe fuel cell is configured to utilize methane as a fuel.
 18. The methodof claim 17 further comprising the methane is provided from landfillgas.
 19. The method claim 13 further comprising steam reforming in thesynthesis gas production unit.
 20. A method of producing CO₂, the methodcomprising: using electricity form a first electricity source to produceoxygen with an oxygen separation unit, wherein the first electricitysource is a renewable energy source; storing a portion of the oxygenproduced in the oxygen separation unit for later used when a level ofelectricity from the first electricity source decreases; using at leastsome of the oxygen in a chemical reaction to produce CO₂ from a reactionwith a hydrocarbon feedstock.
 21. The method of claim 20 wherein storinga portion of the oxygen includes cryogenically storing the portion ofthe oxygen.
 22. The method of claim 20 further comprising usingelectricity from a second source when the electricity from the firstelectricity source varies, wherein the second source includes one ormore of an engine generator, a gas turbine, or fuel cell configured touse methane as a fuel.
 23. The method of claim 22 where the hydrocarbonfeedstock includes a biomass.
 24. A method of treating a hydrocarbonmaterial, the method comprising: introducing hydrocarbon material into amolten bath; electrically heating the molten bath with electricity froma first electricity source; wherein the first electricity sourceprovides electricity from a renewable energy source; electricallyheating the molten bath with electricity from a second electricitysource when the electricity from the first electricity sources varies,wherein the second electricity sources includes one or more of an enginegenerator, a gas turbine or a fuel cell configured to use methane as afuel; and pyrolyzing the hydrocarbon material the molten bath.
 25. Themethod claim 24 where the molten bath contains slag.
 26. The method ofclaim 24 further comprising removing carbon from the hydrocarbonfeedstock in the molten bath.